Method of establishing and/or operating a bore well in a seabed and a drilling vessel for use in connection therewith

ABSTRACT

A bore well in a seabed ( 27 ) may be established and/or operated by a drilling barge ( 10 ). The barge may be pulled onto a larger vessel ( 11 ) and transported to a drilling site. Alternatively, the larger vessel is divided longitudinally into a pair of sub-vessels, which are then re-united at the drilling site, where the barge is pulled into position on the larger vessel. The combined drilling vessel ( 10, 11 ) may thereafter be anchored in the desired position relative to the bore well by submerging the larger vessel to rest on the seabed. The barge may be arranged on top of the larger vessel by submerging one end of the larger vessel, towing the barge into a desired position relative to the larger vessel, and raising the submerged end of the larger vessel so as to bring the deck of the larger vessel into contact with the bottom of the barge and to lift the barge out of the water.

The present invention relates to a method of establishing and/oroperating a bore well in a bed or floor under a body of water by meansof a drilling barge having a derrick and associated drilling equipment.Such drilling barges may be used for drilling in shallow and calm waterareas, such as shallow lakes, river mouths etc. When a drilling barge isto be moved from one drilling site to another distant location it cannot be moved over rough waters.

The present invention provides a method, which may improve the usabilityof a drilling barge. Thus, the present invention provides a method ofestablishing and/or operating a bore well in a bed or floor under a bodyof water by means of a drilling barge having a derrick and associateddrilling equipment, said method comprising: arranging the drilling bargeon top of another, larger floatable vessel, moving the floatable vesselto a location of operation, and anchoring the drilling barge in relationto a bed under said body of water so as to substantially align thederrick with an existing or planned bore well.

By using the method according to the invention an existing drillingbarge may be made more versatile. While the existing drilling equipmentand auxiliary equipment on the drilling barge may be fully utilised, thelarger vessel on which the barge is arranged may lift the derrick to anelevated position, whereby also existing bore wells extending downwardsfrom a platform positioned well above the water surface may be servicedand operated. Furthermore, because the drilling barge is arranged on topof a relatively large vessel anchored to the seabed or sea floor, thedrilling barge may be used also in less calm and deeper areas than ifthe barge had been used separately. Finally, the larger vessel carryingthe drilling barge may be used as a means of transportation, which ismore resistant to less favourable weather conditions than the drillingbarge in itself.

The drilling barge may be positioned on the other floatable vessel inany known manner, for example by means of a stationary or floatingcrane. However, according to the invention the arranging step mayinclude submerging at least one end of the larger vessel, towing thedrilling barge into a desired position in relation to the larger vessel,and raising the submerged end of the larger vessel so as bring the deckof the larger vessel into contact with the bottom of the drilling bargeand to lift the drilling barge out of the water.

The larger vessel may be submerged and later raised by pumping waterinto and out from selected water tanks or chambers contained in thelarger supporting vessel. Therefore, the drilling barge may bepositioned on top of the other vessel, such as a larger barge or anothership, exclusively by means present on the larger vessel. It is possibleto submerge the whole supporting vessel. However, it is more preferredto submerge only the end of the vessel on which the drilling bargeshould be positioned. Thus, the stern of the larger vessel may besubmerged and the drilling barge may thereafter be towed into the saidposition by towing means arranged on the larger vessel. The towing meansmay, for example, be a winch with a wire, which may be connected to thestem of the drilling barge. The drilling barge is preferably towed orpulled to a position in which the major part is supported on the deck ofthe larger vessel, while the part of the drilling barge carrying thederrick and other drilling equipment extends beyond the stern of thelarger supporting vessel.

The larger vessel carrying the drilling barge may be floating when theequipment on the drilling barge is operating for drilling a bore hole orbore well in the sea floor or for operating or servicing an existingbore well. In such case the anchoring of the drilling barge includesanchoring of the larger vessel in relation to the bed under the body ofwater, the drilling barge being fastened immovably in relation to thevessel. The larger floatable vessel may be anchored to the sea floor bymooring lines or other known anchoring means. Such anchoring means maybe of the quick-release type such that the drilling vessel may bereleased quickly if required due to weather conditions or for otherreasons. However, alternatively or additionally anchoring may beobtained by submerging the larger vessel so as to position the vessel incontact with said bed, whereby a very stable positioning of the vesselin relation to the sea floor may be obtained.

In order to allow selective adjustment of the height of the lower end ofthe derrick in relation to the water surface or existing bore wellinstallations supporting spacing means may be arranged between thedrilling barge and the larger vessel, so as to position the drillingbarge and the drilling equipment thereon in a desired position inrelation to the bed or installation. Such spacing means may bereplaceable spacing members. In the preferred embodiment, however, thespacing means may comprise hydraulic rams for adjusting the height ofthe drilling barge and of the derrick positioned thereon.

The drilling barge occupies only a minor part of the deck space of helarger vessel. Therefore, a crane may be positioned on the deck of thelarger vessel and may be used for preparing the drilling site, such asfor replacing damaged or defective parts of bore well installations.

Even though the main purpose of the larger vessel is to support thedrilling barge it may also be used for transporting the drilling bargefrom one location to a distant second location or drilling site. Becausethe larger vessel is more seaworthy than the drilling barge the combinedvessel may be towed over more rough waters than the separate drillingbarge. However, when the transport takes place along more calm waterwaysit may be preferred to tow the drilling barge and the larger vesselseparately, and if the waterways are so narrow that the larger vessel isnot allowed to pass as a separate unit, the larger vessel may be dividedlongitudinally into two separate sub-vessels so as to allowtransportation of the vessel on rivers and other narrow waterways, thesub-vessels being subsequently reunited to re-establish said vessel,whereupon the drilling barge may be lifted or pulled into position ontop of the large vessel so as to establish the combined drilling vessel,which may then be put into operation. The sub-vessels may advantageouslybe reunited by pulling them together by means of wires and associateddrawing equipment, such as anchor winches, bollards and other standardmarine equipment arranged on these sub-vessels.

The drilling barge may later again be disconnected from the largervessel and used separately at said second drilling site, when the heightor depth of the water body does no exceed a predetermined low value, andwhere larger waves do not occur.

The larger vessel does not function only as a support or base for thedrilling barge, but the space on deck of the larger vessel not occupiedby the drilling barge may be used for several other useful purposes insupport of the activities performed by the equipment on the drillingbarge. As examples such space may be used for personnel accommodationstorage area and/or workshop area, etc. to support various offshoreoperations.

The method according to the invention may be used in connection withdrilling and related activities, including activities in connection withthe preparation, operation and service of production wells. Thus, as anexample, the combined drilling barge and larger vessel may be used forassembling and laying a pipeline on the seabed below the body of water,pipe lengths from the storage area being interconnected at the workshoparea so as to form a pipeline, which is gradually immersed into the bodyof water as it is being formed. Preferably, when the pipeline is beingimmersed it may pass through a tensioning system suspended in thederrick of the drilling barge.

The present invention further provides a drilling vessel comprising adrilling barge having a derrick and associated drilling equipment, and alarger supporting floatable vessel, which is adapted to receive thedrilling barge on its upper deck in a position in which the drillingbarge part carrying the derrick extends beyond the deck of thesupporting vessel, means being provided for interconnecting the drillingbarge and the supporting vessel in said position. The drilling vessel,which may, for example, be used in carrying out the method according tothe invention, and the drilling vessel may be constructed and equippedas described above. Furthermore, the larger vessel may comprise towingor pulling means for towing or pulling the drilling barge into positionon the deck of the larger vessel as described above.

The drilling vessel may comprise means for anchoring the supportingvessel in relation to the seabed. Such anchoring may comprise mooringlines of known types. Alternatively or additionally, the anchoring meansmay comprise means for submerging the supporting vessel so as toposition said vessel in contact with the seabed. Such submerging meansmay comprise one or more water tanks or chambers within the supportingvessel and means, such as pumps, for selectively letting water into thetank or tanks and for removing water from the tanks.

The drilling vessel may comprise supporting spacing means arrangedbetween the drilling barge and the supporting vessel, so as to positionthe drilling barge and the drilling equipment thereon in a desiredposition in relation to the seabed, and such spacing means may comprisehydraulic rams or jacks for adjusting the height of the drilling bargeand of the derrick positioned thereon.

The supporting vessel may advantageously be divided longitudinally intotwo separate sub-vessels, so as to allow transportation of the vessel onrivers and other narrow waterways. The supporting vessel may be anexisting conventional vessel or large barge, which has been cutlongitudinally into two separate parts being reconstructed so as to formtwo individually floatable vessels. These sub-vessels are then providedwith connection means, which are preferably releasable. These connectionmeans may comprise wire-pulling means being mounted on the sub-vesselsfor pulling the sub-vessels together. Thus, the sub-vessels may bereunited and form a combined supporting vessel without any requirementfor docking or support from a shipyard.

According to another aspect, the present invention relates to a use of afloatable vessel for carrying or supporting a smaller drilling barge,while the drilling barge is being used for performing drillingoperations. The larger supporting vessel may be floating when thedrilling equipment on the drilling barge is operating. However, whenpermitted by the conditions at the drilling site the larger vessel ispreferably submerged.

According to a further aspect the present invention provides a method ofestablishing and/or operating a bore well in a bed or floor under a bodyof water at a selected location of operation by means of a drillingbarge or vessel having a derrick or rig and associated drillingequipment, said method comprising: providing a plurality of separate,floatable sub-vessels at a first location remote to the selectedlocation of operation, towing the sub-vessels from the remote firstlocation to a second location adjacent to or closer to the selectedlocation of operation, interconnecting the sub-vessels at said secondlocation so as to form a barge, mounting the derrick or rig andassociated drilling equipment on the barge thus formed, moving thedrilling barge to the selected location of operation, and anchoring thedrilling barge in relation to the bed or floor under said body of waterso as to substantially align the derrick with the existing or plannedbore well.

Thus, instead of positioning a smaller drilling barge on top of a largerbarge as explained above, a drilling rig or a derrick and associateddrilling equipment may be mounted directly on the deck of the largerbarge, which is divided into interconnect able sections or sub-vessels.Thus, the drilling barge may be produced in a shipyard at a location faraway from the place where the drilling barge is to be used. Thefloatable sub-vessels may then be towed or transported otherwise to alocation, where the sub-vessels may be assembled to form a barge. Theassembling is preferably performed at or close to the location at whichthe drilling barge is to be used.

The size and dimensions of the sub-vessels may be chosen depending onthe intended means of transportation to the location of operation of thedrilling barge. As an example, the size and dimensions of thesub-vessels may be chosen so as to allow towing or tugging of thesub-vessels on rivers and other narrow waterways by means of a tugboat

The sub-vessels being interconnected preferably comprise a number ofelongated first sub-vessels arranged in side-by-side relationship andextending in the longitudinal direction of the barge. In order tofurther strengthen such structure the sub-vessels may further comprise apair of second sub-vessels being arranged fore and aft, respectively, atthe ends of the first sub-vessels so as to extend transversely to thefirst sub-vessels.

The sub-vessels are preferably at least partly floating when they arebeing assembled. Therefore, as an initial step they may be drawntogether by means of drawing equipment, which may or may not beassociated with the sub-vessels, such as winches, hydraulic cylinders,etc., and subsequently temporarily interconnected by mechanicalinterlocking means, such as books latches, or the like. When such aninterim interconnection has taken place the sub-vessels may beinterconnected more permanently, for example by welding. Each pair ofadjacent sub-vessels are preferably welded together adjacent to the decklevel and adjacent to the bottom level, respectively. In order tofacilitate the welding operation the adjacent sub-vessels are preferablymutually spaced in their said temporarily interconnected condition. Thismay, for example, be obtained by means of connecting flanges, which areformed on and extend outwardly from the sub-vessels so as to bridge saidspacing, whereby the flanges may function as spacing means. Thelowermost flanges are preferably positioned above the water levelallowing a person to move within the space defined between adjacentsub-vessels and to weld each flange on one sub-vessel to the adjacentsub-vessel. Thereby the sub-vessels may be permanently interconnected bydry welds within the protected area formed by the space between theadjacent sub-vessels.

The rig or derrick used on the drilling barge according to the inventionmay be of any suitable type, such as the usual land-based type. The rigand other necessary drilling equipment may be disassembled to an extentallowing the desired manner of transportation, such as by land, seaand/or river, to the place where the drilling barge is to be assembled.Alternatively, however, the rig or derrick may be mounted on the bargeby arranging a smaller drilling barge comprising such rig or derrick andassociated drilling equipment on the deck of the larger barge. Therebyan existing small drilling barge may be used in combination with alarger barge being composed by a number of sub-vessels as explainedabove.

When the drilling barge has completed its mission and is to be used atanother remote drilling site, the more permanent interconnections orwelds between adjacent sub-vessels may be cut or separated so as todivide the barge into said sub-vessels. Thereafter, the sub-vessels maybe towed along rivers or other narrow waterways to the new site ofoperation.

The present invention further provides a drilling barge comprising: aplurality of separately floatable, sub-vessels having tanks formedtherein, each sub-vessel having connecting means for interconnecting thesub-vessels in a floating condition and each sub-vessel defining a deckpart and a bottom part forming in the interconnected condition of thesub-vessels the deck and the bottom, respectively, of the barge, and adrilling rig or derrick to be mounted on the deck of the barge.

The rig or derrick may be positioned at the aft part of the barge so asto extend beyond the outer limits of the barge. In the preferredembodiment, however, the rig or derrick is positioned above and inalignment with a through opening or cutout defined in the barge. Thebarge may further comprise all accessories necessary for performingdrilling operations and/or production of petroleum products, wherebydrilling operations and oil production is possible also in very remoteareas where support and supplies can not be obtained easily.

The invention will now be further described with reference to thedrawings, wherein

FIG. 1 is a side view of an embodiment of the drilling vessel accordingto the invention comprising a drilling barge arranged on top of a largervessel,

FIG. 2 is a side view illustrating how the drilling barge may be movedto a position on the deck of the larger vessel,

FIG. 3 is a top view of a second embodiment of the drilling vesselaccording to the invention separated into three units,

FIG. 4 is a top view illustrating how the sub-vessels into which thelarger vessel is divided may be reunited so as to form a vessel forsupporting the drilling barge,

FIG. 5 is a side view showing the drilling vessel according to FIG. 1 inoperation,

FIG. 6 is a top view of a drilling vessel according to the invention inoperation,

FIG. 7 is a side view of a drilling vessel according to the inventionprovided with a crawling crane on the deck of the larger vessel,

FIGS. 8 and 9 are top and end views, respectively, showing the drillingvessel shown in FIG. 7 in operation,

FIGS. 10 and 11 are side and top views, respectively, of a drillingvessel in accordance with the invention being used for laying a pipelineon the sea floor,

FIG. 12 is a top view of a further embodiment of the drilling vesselaccording to the invention,

FIG. 13 is a side view of a still further embodiment of the drillingbarge according to the invention,

FIG. 14 is a top view of the drilling barge shown in FIG. 13,

FIG. 15 is a sectional view along the line 15—15 in FIG. 14,

FIG. 16 is an exploded top view of the hull of the barge shown in FIGS.13 and 14 illustrating the sub-vessels forming the barge hull,

FIGS. 17, 17 a, and 17 b diagrammatically show a bottom view, alongitudinal sectional view along the line A—A, and a cross-sectionalview along the line B—B, respectively, of the hull of the barge shown inFIGS. 13-15 illustrating the arrangement of tanks defined within thevarious sub-vessels,

FIGS. 18-22 illustrate various steps of interconnecting adjacentsub-vessels, and

FIG. 23 is a cross-sectional view in an enlarged scale of the weldindicated by a dotted circle in FIG. 22.

FIGS. 1-12 illustrate embodiments of the drilling vessel according tothe invention each comprising a conventional drilling barge 10 of thetype used for drilling operations in shallow water areas and a largervessel or barge 11. The drilling barge 10, which is positioned on thestern end of the deck of the larger vessel 11, comprises a derrick 12with a drill floor 13. The drilling barge is also provided withconventional drilling equipment necessary to perform a drillingoperation. The drilling barge may further be provided with cranes 14,accommodation 15 for crew, etc. The larger vessel 11 may be a largerbarge, but may in principle be any other type of vessel or ship being ofa suitable size and having a deck area adapted to receive the drillingbarge 10. The vessel 11 preferably contains a number of tanks orchambers 16 and pumps (not shown), for selectively pumping water intoand out of any of such tanks.

The drilling barge 10 and the larger vessel are separate units, whichmay operate independently. However, in order to increase the versatilityand usefulness of the drilling barge it may be moved to a position onthe deck of the larger vessel 11. FIG. 2 illustrates how the drillingbarge 10 may be conveniently moved onto the deck of the vessel 11. Whilethe drilling barge 10 is floating at the water surface 17 the stern endof the vessel 11 is submerged by pumping water into the after tanks orchambers 16. Now, the stern of the barge 10 is connected to a tuggingwire 18 from a winch 19, and the floating drilling barge 10 is pulled toa position immediately above the submerged after deck part 20 of thevessel 11, vide FIG. 2. This after deck part 20, which is adapted tosupport the drilling barge 10, is defined by means of uprights 21, whichmay be in the form of spacing means such as hydraulic rams, extendingfrom the deck of the vessel 11. When the barge 10 is in the desiredposition the stern end of the vessel 11 is raised by pumping water outof the tanks 16, whereby the barge 10 is positioned on the after part ofthe deck of the vessel 11 so that the drill floor 13 with the derrick 12extends beyond the stern of the vessel 11. The combined drilling vesselmay now be towed to a drilling site by means of a tugboat, or the vesselmay be provided with other kinds of propulsion means, such as anoutboard motor.

In some cases the drilling vessel has to be transported through riversystems or other narrow waterways in order to arrive at the drillingsite. If the larger supporting vessel 11 is too broad to pass suchwaterways it may be divided into a pair of sub-vessels 11′ and 11″ alonga central, longitudinal plane. This means that the drilling vesselaccording to the invention may be divided into three units asillustrated in FIG. 3, namely a conventional drilling barge 10 shown inFIG. 3a and two sub-vessels 11′ and 11″ illustrated in FIGS. 3b and 3 c,respectively. As indicated by arrows 22 each of the units 10, 11′ and11″ may separately be towed to a site of operation, for example throughriver systems by means of a suitable tug vessel, not shown.

When the separate units shown in FIG. 3 have arrived at theirdestination the two sub-vessels 11′ and 11″ may be re-united so as toform the larger supporting vessel 11. As shown in FIG. 4 this may bedone by pulling the sub-vessels together by means of wires 23 andassociated winches 24 mounted on the decks of the sub-vessels 11′ and11″. Thus, the free end of a wire from a winch mounted on one of thesub-vessels is connected to the other sub-vessel, whereby thesub-vessels may be pulled together by operating the winches 24.Furthermore the contacting surfaces of the sub-vessels may be providedwith releasable locking means including locking projections 25 andcomplementary shaped indentations 26 for receiving the projections 25.When the sub-vessels 11′ and 11″ have been interconnected the drillingbarge 10 may be arranged on the deck of the now formed larger vessel 11,where after the drilling vessel thus formed is ready for operation.

FIG. 5 illustrates how a drilling vessel according to the invention maybe used in connection with a bore well in the seabed or sea floor 27.The oil well comprises a well tube 28, which is provided with aso-called “Christmas Tree” 29, and a drilling platform 30. The drillingvessel is positioned such that the well tube 28 and the derrick 12 ofthe barge 10 are substantially co-axial. In FIG. 5 the drilling vesselis floating and is maintained in the desired position by a plurality ofmooring lines, not shown, extending between the supporting vessel 11 andanchors located at the sea floor 27. If the conditions at the drillingsite permit a better “anchoring” of the drilling vessel may be obtainedby locating the supporting vessel 11 in a submerged position in whichthe bottom of the vessel 11 is resting on the sea floor 27 asillustrated in FIG. 1. This may be obtained by reducing the buoyancy ofthe vessel 11 by pumping water into the tanks or chambers 16. It shouldbe understood that the drilling vessel according to the invention may beused not only for drilling operations and associated operations, such aspositioning of lining tubes in the bore well, but also for servicing andrepair.

FIG. 6 shows a drilling vessel according the invention in operation inan oil field, which comprises an accommodation platform 31, a productionplatform 32 from which a number of pipelines 33 extend along the seafloor 27, and a drilling platform 34. The drilling vessel is positionedand anchored (with the supporting vessel 11 floating or submerged) insuch a position in relation to the drilling platform 34 that the drillfloor 13 is located vertically above the bore well of the drillingplatform 34.

FIGS. 7-9 shows a drilling vessel as that shown in FIGS. 1 and 2, butprovided with a crawler crane 35 movable on the fore end of the deck ofthe supporting vessel 11. FIG. 8 is a top plan view illustrating the oilfield shown in FIG. 6 and how the crawler crane 35 may be used forrepairing a possibly damaged drilling platform 34. FIG. 9 is an end viewillustrating the same situation.

FIGS. 10 and 11 illustrate how the drilling vessel shown in FIGS. 7-9may also be used for assembling tube sections 36 from a stock 37 so asto form a pipeline 38, which is currently positioned on the sea floor27. The pipeline formed may pass through a tensioning device 39, whichis suspended from the derrick 12 in a wire 40. The drilling vessel ismoving forwards with a speed corresponding to the rate at which thepipeline 38 is formed.

FIG. 12 is a top plan view of a further embodiment of the drillingvessel according to the invention, where the fore end of the deck of thesupporting vessel 11 is utilised in a different manner. In FIG. 12 thedeck of the vessel 11 not occupied by the drilling barge 10 is used foraccommodation containers 41, workshops and/or as a storage area 42 tosupport various offshore operations. Depending on the intended useadditional containers, racks for storing for example tube sections, etc.could be installed.

FIGS. 13-23 illustrate a further embodiment of the method and drillingvessel according to the invention, and parts similar to those of theembodiments described above are designated by similar reference numbers.In contrast to the embodiments with reference to FIGS. 1-12, in whichexisting vessels not especially designed for the purpose are used, FIGS.13-17 illustrate a drilling vessel comprising a specially designed barge11. As illustrated in FIG. 16 the barge 11 is composed by a number (inthe present embodiment four) of longitudinal sub-vessels 43 and a number(in the present embodiment two) of transverse sub-vessels 44. Each ofthe sub-vessels 43 and 44 has one or more tanks or chambers 16 and is afloatable, self-supporting vessel. Thus, the sub-vessels 43 and 44 maybe towed from one location—for example the shipyard, where they havebeen produced—to a remote location, where the drilling barge is to beused.

When a drilling barge 11 as that shown in FIGS. 13 and 14 is to be usedfor drilling operations in shallow water at a remote location thesub-vessels 43 and 44 may be towed to the location of use by means of atugboat, for example via rivers or other narrow waterways where theassembled barge 11 would not be able to pass. The rig 12, cranes 14, 35and other accessories may also be transported along the same waterwaysor over land in a disassembled condition. When the sub-vessels 43 and 44have arrived at the location of operation or at another location fromwhich the assembled barge 11 may be towed to the location of use, thesub-vessels 43 and 44 may be assembled so as to form the barge 11 shownin FIGS. 13 and 14.

The manner in which a pair of longitudinal sub-vessels 43 may beassembled is illustrated in FIGS. 18-22. As a first step, thesub-vessels floating in water is pulled towards each other by means of awire/winch arrangement 45 mounted at the upper deck 46. When thesub-vessels have been moved sufficiently close to each other they areinterconnected by a number of hydraulic jacks 47 as shown in FIG. 19. Asshown in FIGS. 18-22 one of the sub-vessels 43 has a protruding bottomflange 48 such that a space or cofferdam 49 is defined between adjacentsidewalls of the sub-vessels 43 when they have been pulled together. Inthis position the sub-vessels may be locked together by mechanicallocking means 50. The flange 48 is positioned such that at least theupper part of the flange is above the water surface level 17 and awelding operator may now permanently interconnect the sub-vessels 43 bymeans of weld seams 51. It is a big advantage that the welding operationmay take place within the cofferdam 49 so that the sub-vessels may beassembled by a “dry” weld while they are floating. Thus, it is neithernecessary to bring the sub-vessels to a dry dock—if at all available—norto weld under water by divers, which would be more costly and reduce thequality of the weld. Finally, the upper part of the cofferdam 49 may beclosed by a plate member 52 being welded to the upper deck 46, forexample as illustrated in FIGS. 21 and 22 and more in detail in FIG. 23.

When all of the longitudinal sub-vessels 43 have been interconnected inthis manner, the transverse sub-vessel 44 may be connected to the endsof the interconnected sub-vessels 43 for and aft in a similar manner.The barge hull now produced has an upper deck 46, a flat bottom 53 andupwardly and inwardly sloping side surfaces 54, which are suited towithstand ice formations. The shape of the sloping side surfaces is bestshown in FIG. 15. A derrick or rig 12, which may, for example be of theland based type, and conventional accessories may now be mounteddirectly on the upper deck 46 of the barge hull formed such that the rigor derrick 12 is aligned with a through opening 55 defined in the hullof the barge 11, see FIGS. 14, 16 and 17. Cranes 14 and 35, a helicopterdeck 46 a and other equipment conventionally used on a drilling vesselmay also be placed or mounted on the upper deck 46.

When the drilling barge 11 thus produced has been positioned at thedrilling site water may be pumped into at least some of the internaltanks or chambers 16 so as to place the flat bottom 53 of the barge 11in contact with the sea floor 27 and/or the barge 11 may be held inposition by mooring lines 56, see FIG. 14.

FIGS. 17, 17 a and 17 b illustrates a possible arrangement of tanks orchambers defined within the hull of the drilling barge 11.

EXAMPLE 1

An offshore oil field at Bahrgansar in Iran comprises three platformssituated on piles, namely (as shown in FIG. 8) an accommodation platform31, a production platform 32 and a drilling platform 34. The oil fieldfurther comprises six satellite platforms each having one well and apipeline to the production platform. The water depth in the area isvarying from about 4.5 m to about 8 m. During the war between Iran andIraq the drilling platform was severely damaged and approximately halfof the drilling platform is now gone with only the rammed piles left.Also the derrick and the drill floor are badly damaged and beyondrepair. A lot of fragments from bombing and the resulting fire havedamaged the remaining platform. The wellheads are not damaged. Theproduction platform is still producing and the other two wells wereplugged, but with moderate success only. Thus, a lost piece of drillpipe is left in one of these wells and in the other well a 900 m longdrill string is hanging in the slips.

It is proposed to bring the above mentioned oil field to its fullproduction level by means of a drilling vessel according to the presentinvention as illustrated in FIGS. 1, 2 and 5-12. It is possible to usean existing drilling barge 10 presently located in Venezuela, becausewhen the barge 10 is placed on the deck of the larger vessel 11 it ispossible to tow the combined drilling vessel to the oil field in Iran.

The main particulars of the drilling vessel thus provided may be asfollows:

overall length 135 m overall width 30.5 m lightweight 5,880 metrictonnes accommodation 70 men (upgraded from 38 men) rated drilling depth6,095 m (20,000 feet)

Particulars of main drilling equipment may be as follows:

derrick DRECO 147 ft., 1000,000 lbs. capacity mud pumps 2 x OilwellA-1700-PT rotary table Oilwell B37½″ w/electric drive drawworks OilwellE-2000 with Elmagco electric brake

Operating environmental criteria:

maximum winds speed 20 m/s water depth + spring tide + penetration 10.7m of vessel 11 into sea floor maximum

The above oil field may be repaired and overhauled by means of thedrilling vessel specified above and possibly provided with a crawlercrane 35 as shown in FIGS. 7-9. Thereafter the damaged derrick and drillfloor of the drilling platform 34 may be replaced by the derrick 12 andthe drill floor 13 of the drilling barge 10, so that drilling operationsmay take place. The satellite platforms are located where the waterdepth is 4-5 m, and the above-specified drilling vessel also providessufficient drill floor height over the satellite platforms even when thelarger supporting vessel 11 is submerged and is resting on the seafloor. Furthermore, the derrick 12 of the drilling barge 10 may be usedfor positioning and piling new satellite platforms.

EXAMPLE 2

It is planned to drill several exploration wells in the shallow waterareas in the Caspian Sea. For this purpose a drilling vessel accordingto the invention comprising the drilling barge 10 specified in Example 1could conveniently be used. It is proposed to place the drilling barge10 on a larger transporting vessel 11 in Venezuela and to tow thecombined vessel to a suitable shipyard in the Baltic or Black Sea, wherethe transporting and supporting vessel 11 is cut longitudinally in twohalves, and new longitudinal bulkheads will be installed to allow thesections of the larger barge or vessel 11 to be towed as separatevessels or sub-vessels 11′ and 11″ (FIG. 3) each with their own powergenerators, pumps, navigational lights etc. Furthermore, the sub-vesselsmay be provided with simple mechanical interlocking systems as describedabove in connection with FIGS. 3 and 4.

The drilling barge 10 and the sub-vessels 11′ and 11″ may now be towedseparately through the internal Russian river system to a suitablelocation in the Caspian Sea. Without any need for shipyard facilitiesthe sub-vessels may be reunited as described above in connection withFIG. 4, and the drilling barge 10 may be pulled in position on thelarger vessel 11 as illustrated in FIG. 2. Now, the combined drillingvessel may be towed to its first drilling location by means of suitabletugs. At the drilling location the vessel is held in position by meansof mooring lines, and the larger supporting vessel 11 is submerged so asto rest on the sea floor. Then the drilling operation may start.

Field Description

The described drill vessel according to the invention will have accessto the following fields, where the penetration of the supporting vessel11 into the seabed is expected to be between 10 and 40 cm.

Field Water depth Surge range (50 years) Kashagan East (KE) 3.7 m−1.5-1.6 m Kashagan West (KW) 7.2 m −0.9-0.9 m Kalamkas (KL) 9.0 m−0.9-0.9 m

The main particulars of the drilling vessel may be as follows:

overall length 135/122 m overall width 30.5 m height 10.7/12.7/12.2/14.2m lightweight 5,880 metric tonnes accommodation 38 men rated drillingdepth 6,095 m (20,000 feet)

Operating environmental criteria (50 years return period):

maximum winds speed 34 m/s maximum current  1 m/s

The above example illustrates the flexibility or versatility of thedrilling vessel according to the invention allowing an existing drillingbarge 10 to be transported to and utilised at a distant location withvery restricted accessibility.

EXAMPLE 3

The sections or sub-vessels for a multi-section barge of the typedescribed above with reference to FIGS. 13-23 is planned to befabricated, pre-assembled and tested in a shipyard at the Baltic Sea.After disassembling the sections or sub-vessels are towed to the CaspianSea via the river waterways in Russia. As explained previously,re-assembly in the Caspian Sea may be carried out exclusively by usingequipment, such as anchor winches, hydraulic cylinders and pre-installedlocking devices present on the sub-vessels or barge sections. Allstructural assembly welds may be carried out with dedicated, on-boardequipment and in “dry” condition above water level in a 2 m widecofferdam. The barge thus assembled will be provided with an existingarctic (land) rig. The accommodations and the drilling equipment moduleswill be lifted into place using an on-board crawler crane. There-assembly location can thus be any location, which is relativelysheltered in vicinity of a small harbour facility (Bautino, or similar)for temporary storage of various equipment. The drilling barge will betowed to its drilling location with tugboats. For shallow water depthsnot accessible for tugboats, self-contained thrusters (optional) can beused to bring the barge to its final drilling position.

The drilling barge is fully equipped for all-year drilling operations inthe Northern Caspian Sea in water depths ranging from approximately 1.5to 7.4 m. During summertime drilling capability in water depths up to9.0 m is possible, depending on storm surges. When fully assembled andoperational the barge has a total main deck surface area ofapproximately 6,100 m² (bottom area is 9,000 m²), enabling operation forextended periods (up to three months) without supply boat tendering. Forpersonnel emergency evacuation, the use of highly mobile all-terrainamphibious “Arktos” vehicles are envisaged.

It should be understood that the various modification and changes of theembodiments described above could be made without departing from thescope of the present invention.

What is claimed is:
 1. A method of establishing and/or operating a borewell in a bed or floor under a body of water by means of a drillingbarge having a derrick and associated drilling equipment, said methodcomprising the steps of: arranging the drilling barge on top of another,larger floatable vessel; arranging supporting spacing means between thedrilling barge and the larger vessel; moving the floatable vessel to alocation of operation; anchoring the drilling barge in relation to a bedunder said body of water so as to substantially align the derrick withthe existing or planned bore well, said anchoring comprising submergingthe larger vessel so as to position the vessel in contact with said bed;and positioning the drilling barge and the drilling equipment thereon ina desired position in relation to the bed by the supporting spacingmeans.
 2. A method according to claim 1, wherein the step of arrangingthe drilling barge on top of the larger vessel includes the steps of:submerging at least one end of the larger vessel; towing the drillingbarge into a desired position in relation to the larger vessel; andraising the submerged end of the larger vessel so as bring the deck ofthe larger vessel into contact with the bottom of the drilling barge andto lift the drilling barge out of the water.
 3. A method according toclaim 2, wherein the stern of the larger vessel is submerged and thedrilling barge is towed into the said position by towing means arrangedon the larger vessel.
 4. A method according to claim 1, wherein thespacing means comprise hydraulic rams for adjusting the height of thedrilling barge and of the derrick positioned thereon.
 5. A methodaccording to claim 1, wherein a crane positioned on the deck of thelarger vessel and is used for preparing the drilling site.
 6. A methodaccording to claim 1, wherein the larger vessel is used for transportingthe drilling barge from one location to a distant second location.
 7. Amethod according to claim 1, wherein the drilling barge and thefloatable vessel are moved from one location to a distant secondlocation separately, the larger vessel being divided longitudinally intotwo separate sub-vessels, so as to allow transportation of the vessel onrivers and other narrow waterways, the sub-vessels being subsequentlyreunited to re-establish said vessel.
 8. A method according to claim 7,wherein the sub-vessels are reunited by pulling them together by meansof wires and associated drawing equipment arranged on these sub-vessels.9. A method according to claim 1, wherein the drilling barge isdisconnected from the larger vessel and used separately at said seconddrilling site, when the height or depth of the water body does notexceed a predetermined low value.
 10. A method according to claim 1,wherein the space on deck of the larger vessel not occupied by thedrilling barge is used for a purpose selected from the group consistingof personnel accommodation, storage, and workshop.
 11. A drilling vesselcomprising a drilling barge having a part carrying a derrick andassociated drilling equipment; a larger supporting floatable vesselhaving an upper deck that is configured to receive the drilling barge ina position in which the drilling barge part carrying the derrick extendsbeyond the deck of the supporting vessel, means being provided forinterconnecting the drilling barge and the supporting vessel in saidposition; means for anchoring the barge in relation to a seabed bysubmerging the supporting vessel so as to position said vessel incontact with the seabed; and supporting spacing means arranged betweenthe drilling barge and the supporting vessel, so as to position thedrilling barge and the drilling equipment thereon in a desired positionin relation to the seabed.
 12. A drilling vessel according to claim 11,wherein the larger vessel comprises towing means for towing the drillingbarge into position on the deck of the larger vessel.
 13. A drillingvessel according to claim 11, wherein the spacing means comprisehydraulic rams or jacks for adjusting the height of the drilling bargeand of the derrick positioned thereon.
 14. A drilling vessel accordingto claim 11, further comprising a crane positioned on the deck of thesupporting vessel, for use in preparing the drilling site.
 15. Adrilling vessel according to claim 11, wherein the supporting vessel isdivided longitudinally into two separate sub-vessels, so as to allowtransportation of the vessel on rivers and other narrow waterways.
 16. Adrilling vessel according to claim 15, wherein the sub-vessels comprisewire pulling means for pulling the sub-vessels together so as reunitethe sub-vessels and form a combined supporting vessel.
 17. A drillingvessel according to claim 11, wherein part of the deck of the supportingvessel not occupied by the drilling barge is configured for a useselected from the group consisting of personnel accommodation, storage,and workshop.
 18. A method of establishing and/or operating a bore wellin a bed or floor under a body of water at a selected location ofoperation by means of a drilling barge or vessel having a derrick or rigand associated drilling equipment, said method comprising the steps of:providing a plurality of separate, floatable sub-vessels at a firstlocation remote to the selected location of operation, the size anddimensions of each sub-vessel allowing for transportation of thesub-vessels on rivers or other narrow waterways; towing the sub-vesselsfrom the remote first location via such narrow waterway to a secondlocation adjacent to or closer to the selected location of operation;interconnecting the sub-vessels at said second location so as to form abarge; mounting the derrick or rig and associated drilling equipment onthe barge thus formed; moving the drilling barge to the selectedlocation of operation; and anchoring the drilling barge in relation tothe bed or floor under said body of water so as to substantially alignthe derrick with the existing or planned bore well.
 19. A methodaccording to claim 18, wherein the sub-vessels being interconnectedcomprise a number of elongated first sub-vessels arranged inside-by-side relationship and extending in the longitudinal direction ofthe barge.
 20. A method according to claim 19, wherein the sub-vesselsbeing interconnected further comprise a pair of second sub-vessels beingarranged fore and aft, respectively, at the ends of the firstsub-vessels so as to extend transversely to the first sub-vessels.
 21. Amethod according to claim 18, wherein the sub-vessels are drawn togetherand temporarily interconnected by mechanical interlocking means, thesub-vessels subsequently being interconnected more permanently, forexample by welding.
 22. A method according to claim 21, whereinadjacent, temporarily interconnected sub-vessels define a spacethere-between, the sub-vessels being interconnected in such mutualposition by welding the adjacent sub-vessels together within said space.23. A method according to claim 22, wherein the adjacent sub-vessels arewelded together at one or more levels above the water level.
 24. Amethod according to claim 22, wherein the adjacent sub-vessels compriseoutwardly extending spacing means bridging said space between thesub-vessels, the sub-vessels being welded together by welding saidspacing means.
 25. A method according to claim 18, wherein saidanchoring step comprises the step of submerging the drilling barge so asto position its bottom in contact with said bed or floor.
 26. A methodaccording to claim 25, wherein each sub-vessel defines one or more watertanks therein, the barge being submerged by pumping water into at leastsome of said tanks.
 27. A method according to claim 18, wherein the rigis of the land based type.
 28. A method according to claim 18, whereinthe rig or derrick is mounted on the barge by arranging a smaller bargecomprising such rig or derrick and associated drilling equipment on thedeck of the larger barge.
 29. A method according to claim 21, whereinthe more permanent interconnections are separated after completion ofthe operations of the barge so as to divide the barge into saidsub-vessels.
 30. A set of separately floatable sub-vessels for forming adrilling barge or vessel, said set comprising: a plurality of elongatedfirst sub-vessels adapted to be arranged in side-by-side relationship soas to extend in the longitudinal direction of the vessel, the size anddimensions of each sub-vessel allowing for transportation of thesub-vessels on rivers or other narrow waterways, said sub-vessels havingtanks formed therein, and each sub-vessel having connecting means forinterconnecting the sub-vessels in a floating condition and comprisingdrawing equipment for drawing the sub-vessels into mutual adjacentpositions; mechanical interlocking means for temporarily interconnectingthe sub-vessels in such position, and means for subsequentlyinterconnecting the sub-vessels more permanently, each sub-vesseldefining a deck part and a bottom part forming in the interconnectedcondition of the sub-vessels the deck and the bottom, respectively, ofthe vessel; and a drilling rig or derrick to be mounted on the deck ofthe vessel.
 31. A set according to claim 30, wherein the means for morepermanently interconnecting adjacent sub-vessels comprise weldableinterconnecting flanges keeping adjacent sub-vessels mutually spaced intheir interconnected condition.
 32. A set according to claim 30, furthercomprising means for anchoring the assembled vessel in relation to thebed or floor under a body of water.
 33. A set according to claim 32,wherein said anchoring means comprise means for submerging the vessel soas to position the bottom surface of the vessel in contact with the bedor floor.
 34. A set according to claim 33, wherein the submerging meanscomprise pumping means for pumping water into the water tanks of thesub-vessels.
 35. A set according to claim 30, wherein the bottom partsof the sub-vessels define a flat bottom of the vessel in their assembledcondition.
 36. A set according to claim 30, wherein the sub-vessels tobe interconnected further comprise a pair of second sub-vessels to bearranged fore and aft at the ends of the first sub-vessels so as toextend transversely to the first sub-vessels.
 37. A set according toclaim 30, wherein the sub-vessels adapted to be arranged fore, aft andat the sides of the assembled vessel define sloped outer side surfacesbeing able to withstand ice forces.
 38. A set according to claim 30,wherein the rig or derrick is positioned at the aft part of theassembled vessel above and in alignment with a through opening definedin the vessel.
 39. A set according to claim 30, further comprising asmaller drilling barge to be arranged on top of the larger vessel formedby the sub-vessels, the rig or derrick being mounted on the smallerdrilling barge.
 40. A set according to claim 30, further comprisingaccessories necessary for performing drilling operations and/orproduction of petroleum products.